Fluid couplings

ABSTRACT

A scoop-trimmed fluid coupling is modified by increasing the size of its baffle, drilling two sets of holes in the impeller wall and altering the numbers of vanes on the impeller and the runner. A substantially constant output torque is maintained when accelerating a load simply by increasing the filling when the input torque drops but otherwise holding the filling constant.

United States Patent 11 1 1111 3,919,844 Elderton Nov. 18, 1975 FLUIDCOUPLINGS 2,357,485 9/1944 Miller 60/366 3,037,459 6/1962 Nelden 60/367x [75] Inventor: John Eldemn Hampton 3,190,076 6/1965 Meyer et al 60/351England [73] Assignee: Fluidrive Engineering Company Limited, Isleworth,England Filed: Aug. 7, 1974 Appl. No.: 495,470

Foreign Application Priority Data Aug. 9, 1973 United Kingdom 37840/73US. Cl. 60/330; 60/347; 60/351; 60/365 Int. Cl. F16D 33/00 Field ofSearch 60/327, 330, 334, 347, 60/351, 352, 357, 365

References Cited UNITED STATES PATENTS 11/1942 Sinclair 60/365 PrimaryExaminerEdgar W. Geoghegan Attorney, Agent, or Firm-Woodhams, Blanchardand Flynn [57] .ABSTRACT A scoop-trimmed fluid coupling is modified byincreasing the size of its haffle, drilling two sets of holes in theimpeller wall and altering the numbers of vanes on the impeller and therunner. A substantially constant output torque is maintained whenaccelerating a load simply by increasing the filling when the inputtorque drops but otherwise holding the filling constant.

12 Claims, 9 Drawing Figures US. Patent Nov. 18, 1975 Sheet 1 of93,919,844

US. Patent Nov. 18,1975 Sheet20f9 3,919,844

US. Patent Nov. 18, 1975 Sheet 3 of9 3,919,844

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FIG. 6

US. Patent Nov. 18, 1975 Sheet 8 of9 3,919,844

FLUID COUPLINGS This invention relates to fluid couplings of the kindcomprising vaned impeller and runner elements which together define atoroidal working circuit for a liquid and in which the degree of fillingof the working circuit can be varied in use. An object of the inventionis to provide a variable-filling fluid coupling which will transmit asubstantially uniform torque whilst accelerating a load, when under thecontrol of a control arrangement for the coupling such that the fillingof the working circuit is increased whenever the transmitted torquefalls below a predetermined value and the filling is held constantwhenever the transmitted torque is not below the predetermined value.One field in which such a requirement arises is to be found in drivesfor long conveyor belts. Such conveyor belts, which may be several milesin length, are used for example for conveying minerals from a mine to arailhead or harbour. Considerable economies can be made in the capitalcost of the conveyor belt by reducing the number of belt plies so thatthe belt will for example withstand forces up to but not greater thansay 50% greater than the normal operating values. To prevent damage tothe belt, the belt drive must be prevented from exerting forces greaterthan 150% of the normal full load value. Another application where thesame requirements apply would be a large fan where the application ofexcessive driving torques could cause damage to the fan. Furthermore, inthe case of electric motor drives, limitation of the maximum torqueapplied to the load and thus of the maximum torque applied to the motorcan prevent undue disturbance of the electrical network and can alsoprevent excessive voltage drop where the electric motor is situated in aremote location requiring long power lines.

According to the present invention, there is provided a variable-fillingfluid coupling typically of the scoop trimming type having a baffle ofdiameter at least 1.25 times the inner profile diameter of the workingcircuit, the runner of the coupling having between and 35% more vanesthan the impeller of the coupling, and the impeller having two sets ofholes drilled therethrough, the centres of one set of holes being spacedfrom the coupling axis by from 53 to 63% of the outer profile radius ofthe working circuit and the centres of the second set of holes arespaced from the coupling axis by from 65 to 75% of the outer profileradius of the coupling. Preferably, the spacing between the two sets ofholes is about 10%, measured in the radial direction of the coupling, ofthe radius of the outer profile of the working circuit.

Preferably the runner has between and 25% more blades than the impeller.In one advantageous embodiment, the baffle has the diameter of 1.3 timesthe inner profile diameter of the working circuit, the two sets of holeshave pitch circle diameters respectively 58 and 70% of the outer profilediameter and the runner has approximately more blades than the impeller.

Embodiments of the invention will now be described by way of examplewith reference to the accompanying drawings in which:

FIG. 1 is an axial sectional view of a scooptrimmed fluid. coupling inaccordance with the invention,

FIG. 2 shows a view of the impeller as seen in the direction of thearrows IIII in FIG. 1,

FIG. 3 is a graph showing the torque coefficient K plotted againstpercentage slip as the coupling accelerates a load from rest tooperational speed, the filling of the coupling being increased wheneverthe transmitted torque falls below a predetermined value K,

FIG. 4 is a graph corresponding to FIG. 3 for a conventional coupling,similar to that shown in FIGS. 1 and 2 but without any of thecharacterising features of the invention,

FIG. 5 shows a similar graph to FIG. 4 for a coupling of conventionalconstruction with the exception of having an enlarged baffle,

FIG. 6 shows a corresponding graph for a coupling having a baffle andpattern of holes in the impeller wall in accordance with the inventionbut having a substantially equal number of vanes on the impeller andrunner,

FIG. 7 shows diagrammatically an installation incorporating the couplingand its control arrangement and FIGS. 8 and 9 are views corresponding toFIGS. 1 and 2 of another coupling in accordance with the invention.

The scoop-trimmed fluid coupling shown in FIGS. 1 and 2 is ofconventional construction in so far as it comprises coaxially mountedinput and output shafts l and 2 interconnected by a ball bearing 3, arotating casing 4 secured to the input shaft 1, a vaned impeller 5secured to the casing 4, a vaned runner 6 secured to the output shaft 2and defining with the impeller 5 a toroidal working circuit W, and atrimming scoop 7 slidably mounted in a stationary structure 8 andprojecting into a scoop chamber 9 defined between the back of theimpeller 5 and a scoop chamber casing 10 secured to the outer peripheryof the rotating casing 4 and to the impeller 5.

The coupling shown in FIGS. 1 and 2 departs however from conventionalpractice in that its baffle l 1 has a radius 1.3 times the inner profileradius 12, as opposed to a more conventional value of 1.1 times theinner profile radius, the impeller 5 has two series of holes 13 and 14drilled through it and the runner 6 has about 20% more vanes than theimpeller. In the particular coupling shown'in FIGS. 1 and 2, the workingcircuit W has an outer profile radius 15 of 5% inches. A conventionalcoupling of this size would have for example 42 vanes'on the impellerand 40 vanes on the runner. In the coupling shown in FIGS. 1 and 2, theimpeller has 45 vanes but the runner has 54 vanes and may be of similarconstruction to the impeller shown in FIG. 2 (the pattern in each of thethree sectors of the coupling being identical) with the exception thatthe three widest pockets 21, 22, 23 formed between the vanes are eachdivided into two pockets by the addition 'of a vane in each of thesepockets. Alternatively, the vanes in both impeller and runner may beequi-spaced.

The two sets of holes, 13, 14 are drilled through the wall of theimpeller. The holes l3, 14 are typically :4 inch in diameter. With theexception of one pocket, alternate pockets each have one hole, either 13or 14. The centres of the holes 13 lie on a circle centred on thecoupling axis and of diameter 6% inches. The centres of the holes 14also lie on a circle centred on the coupling axis of diameter 8% inches.Thus, the holes 13 lie on a circle whose radius is about 58% of theouter profile radius 15 while the holes 14 lie on a circle whose radiusis about of the outer profile radius FIG. 3 shows the K value(proportional to the transmitted torque for a constant motor speed)plotted against the percentage slip for a variety of different loadswhen accelerating a load from rest 100% slip) to full speed. The graphswere obtained with a control system (similar to that shown in FIG. 7)which served merely to move the scoop tube in the direction to increasethe working circuit filling in response to a reduction in thetransmitted torque as measured for example by measuring the currenttaken by a squirrel-cage electric motor driving the coupling. Such acontrol system has no provision for reducing the torque transmitted bythe coupling in the event that the transmitted torque exceeds thepredetermined value. Despite this, it will be noticed that thetransmitted torque does not rise more than about 10% above thepredetermined value. Furthermore, between the lines 31 and 32 thetransmitted torque is particularly constant. The portions of graphs tothe right of the line 31 correspond to the fixed initial position of thescoop which is reached by the scoop on starting up of the system, thisposition corresponding to the degree of filling of the working circuitrequired to transmit the predetermined torque at 100% slip.

In contrast, FIG. 4 shows the corresponding curves obtained with anunmodified coupling. In the region to the right of the line 41, thetransmitted torque rises to a maximum about 50% greater than thepredetermined value. While this may not be detrimental for somepurposes, there are some-applications such as the driving of longconveyor belts having a minimum number of belt plies where the increasein torque during acceleration could cause damage.

Even in the range between the lines 41 and 42, there are appreciablevariations in the transmitted torque, in some cases amounting to morethan 10% of the predetermined value.

The curves in FIG. 5 show the effect of increasing the diameter of thebaffle in an otherwise conventional coupling. While the magnitude of themaximum transmitted torque is somewhat reduced, it still represents avalue some above the predetermined value. Furthermore, although thetorque between the lines 51 and 52 is in general more constant, it willbe seen that there are a number of disturbances such as are shown at 53,54 and 55 which may be unacceptable for some purposes.

FIG. 6 shows the effect of the combination of the larger baffle and thetwo sets of holes in the impeller wall in an otherwise standard couplingin which the impeller has 42 vanes and the runner has 40 vanes. Bycomparison with FIG. 5, it will be seen that the two sets of holesrender the transmitted torque much more uniform over virtually the wholeslip range up to the operating value but there are still a number ofirregularities as shown at 63, 64 and 65. Nevertheless, it will be seenthat the pattern of holes avoids any significant increase in the torquein the high slip range to the right of the line 61.

Comparison of FIG. 6 with FIG. 3 shows that the increase in the numberof vanes in the runner eliminates the irregularities such as those shownat 63, 64 and 65.

FIG. 7 shows diagrammatically an application of the coupling shown inFIGS. 1 and 2, the coupling being indicated at 103.

In the arrangement shown in FIG. 7, a three phase high voltage highpower squirrel cage motor 101 has its output shaft 102 connected to theinput of the scooptrimmed fluid coupling 103, such as that shown in.

FIGS. 1 and 2, the output of which is connected to the load 104 to bedriven. In general, the load 104, for example a long conveyor belt, maybe represented by a flywheel 105 representing the inertia of the loadand a friction brake 106 representing the power dissipated by the loadas the result of friction, air resistance and like losses.

In known manner, the position of the scoop tube 7 determines the degreeof filling of the working circuit W of the coupling 103. The scoop 7 ismovable over its whole range of positions by a small reversible motor111 driving through a reduction gearbox 112.

The torque in the shaft 102 of the motor 101 is approximatelyproportional to the current drawn by the motor 101. This current ismeasured by a pickup coil 113 surrounding one of the leads of thethree-phase electrical supply 114 to the motor 101 and forming with thislead a transformer. The ends of the coil 113 which thus forms thesecondary winding of this transformer, are connected to a currentsensing unit 115 which, when the current in the leads exceeds apredetermined value energizes a relay 116 which in turn deenergizes amotor controller 117 for the motor 111. The current sensing unit 115 isarranged to de-energize the relay 116 when the current in the leads 114falls below tthe predetermined value, thereby re-energizing thecontroller 117 to start up the motor 111 again.

In operation, with the system at rest, the scoop tube 7 of the coupling103 is in its circuit empty position. The motor 101 is switched on andruns rapidly up to its normal speed since the working circuit W of thecoupling 103 is empty. The relatively low voltage supply 121 for themotor 111 is then switched on and the motor 111 is energized by themotor controller 117 to begin to draw the scoop tube 7 out in thedirection of the circuit full position.

As a result, the working circuit W begins to fill and the torque loadimposed on the motor 101 rises. Correspondingly, the current drawn fromthe high voltage supply through the leads 114 rises until its value, assensed by the coil 113 and the current sensing unit 115 reaches apredetermined value, for example or of the normal operational full speedloan value, whereupon the current sensing unit 115 actuates the relay116 to cause the motor controller 117 to stop the motor 111. This inturn stops the scoop tube 7.

The motor 101 then continues to drive the load 104 through the partiallyfilled working circuit W. The torque transmitted by the working circuitW is sufficient to overcome the frictional forces represented by thebrake 106 and to continue to accelerate the load 104 against its inertia(represented by the flywheel 105).

If the characteristics of the coupling 103 are such that as the speedrises, the torque transmitted by the coupling with this particulardegree of filling also rises, then the motor 111 will remainde-energized and although the torque exerted by the motor will increasesomewhat, the filling of the working circuit W will remain constant.When, as a result of increasing speed, the characteristics of thecoupling cause the transmitted torque to fall below the predeterminedvalue, the fall in the current in the leads 114 will be sensed by thecurrent sensing unit which will cause the relay 116 to operate the motorcontrol 117 to drive the scoop tube 7 further towards the circuit fullposition until the predetermined torque value is re-established. Thisonoff switching of the motor 111 continues until the scoop tube 7reaches its circuit full or normal operating position.

The motor 101 then continues to drive the load at normal speed. When themotor 101 is switched off to close down the system, a reversing switch(not shown) for the motor 111 causes the motor 111 to drive the scooptube 7 into its circuit empty position ready for the next time the motor101 is started up.

The fluid coupling shown in FIGS. 8 and 9 differs from that shown inFIGS. 1 and 2 principally in that it is designed to transmit higherpower at higher speeds than that shown in FIGS. 1 and 2. In thisembodiment, the outer profile radius 212 is 8% inches. The axial widthof the working circuit W is slightly greater than its maximum radialdimension.

As in the case of the couplings shown in FIGS. 1 and 2, the couplingsshown in FIGS. 8 and 9 is modified from conventional practice in anumber of respects. Thus, the external diameter of the baffle 211 isincreased from its normal value of 1.1 times the inner profile diameterof the working circuit to 1.25 or 1.3 times the inner profile diameter.For some applications, the value of 1.25 is preferable as it gives aslightly higher maximum starting torque.

Furthermore, the impeller 205 has 45 vanes instead of the conventional51 vanes and the runner 206 has 54 vanes instead of the conventional 48vanes. Two sets of holes 213 and 214 are drilled in the impeller 205with their centres respectively at radial distances of 58% and 70% ofthe outer profile radius 212 from the axis of the coupling.

In addition, the impeller hub has inlet ports 220 which are inclined at45 to the coupling axis instead of the more usual radial disposition.Under some conditions, the inclined disposition of the inlet ports isfound to cause less delay in establishing a stable vortex within theworking circuit when starting.

Care should be taken that there is no excessive loss of working liquidthrough the bearing 203 interconnecting the inlet shaft 201 and theoutlet shaft 202 under the varying operating conditions to beencountered by the coupling. With this in mind, in the arrangement shownin FIG. 8, a single inclined vent passage 221 permits some circulationof liquid through the bearing 203 but has its inner end 222 positionedradially inwards of the balls of the bearing 203. Further, the runningclearance X between the hub of the casing 204 and the shaft 202 isrelatively small, being in this case about 0.0025 inch.

The impeller has twenty-two holes 213 and twentythree holes 214, bothsets of holes being inch in diameter.

I claim:

1. In a variable filling fluid coupling having vaned impeller and runnerelements together defining a toroidal working circuit for a liquid,comprising the improvement wherein the coupling has a baffle of diameterat least 1.25 times the inner profile diameter of the working circuit,the runner of the coupling has between 10 and 35% more vanes than theimpeller of the coupling, and the impeller has two sets of holes throughthe wall thereof, the centres of one set of holes being spaced 6 fromthe coupling axis by from 53 to 63% of the outer profile radius of theworking circuit and the centres of the second set of holes being spacedfrom the coupling axis by from 65 to 75% of the outer profile radius ofthe working circuit.

2. A coupling according to claim 1, wherein the spacing between the twosets of holes is about 10%, measured in the radial direction of thecoupling, of the radius of the outer profile of the working circuit.

3. A coupling according to claim 1 wherein the runner has between 15 and25% more vanes than the impeller.

4. A coupling according to claim 1, wherein the two sets of holes havepitch circle diameters respectively substantially 58% and of the outerprofile diameter of the working circuit, and the runner hasapproximately 20% more vanes than the impeller.

5. A coupling according to claim 1, wherein the baffle has a diameter ofsubstantially 1.3 times the inner profile diameter of the workingcircuit.

6. A coupling according to claim 1, wherein the two sets of holes havepitch circle diameters respectively substantially 58% and 70% of theouter profile diameter, and the runner has between 15% and 25% morevanes than the impeller.

7. A coupling according to claim 6, wherein the baffle has a diameter ofsubstantially 1.3 times the inner profile diameter of the workingcircuit.

8. A coupling according to claim 1, wherein the spacing between the twosets of holes is about 10%, measured in the radial direction of thecoupling, of the ra dius of the outer profile of the working circuit,and wherein the runner has between 15% and 25% more vanes than theimpeller.

9. In a variable filling fluid coupling having vaned impeller andrunning elements together defining a toroidal working circuit for aliquid, comprising the improvement wherein the coupling has a baffle ofdiameter greater than the inner profile diameter of the working circuitto minimize the maximum torque generated by the coupling when driving aload, the runner of the coupling has between 10 and 35% more vanes thanthe impeller of the coupling, and the impeller has two sets of holesthrough the wall thereof, the centres of one set of holes being spacedfrom the coupling axis by from S3 to 63% of the outer profile radius ofthe working circuit, and the centres of the second set of holes beingspaced from the coupling axis by from 65 to %-of the outer profileradius of the working circuit.

10. A coupling according to claim 9, wherein the runner has between 15%and 25% more vanes than the impeller.

11. A coupling according to claim 9, wherein the centres of said one setof holes are spaced from the coupling axis by about 58% of the outerprofile radius of the working circuit, and wherein the centres of saidsecond set of holes are spaced from the coupling axis by about 70% ofthe outer profile radius of the working circuit.

12. A coupling according to claim 11, wherein the runner has about 20%more vanes than the impeller.

1. In a variable filling fluid coupling having vaned impeller and runnerelements together defining a toroidal working circuit for a liquid,comprising the improvement wherein the coupling has a baffle of diameterat least 1.25 times the inner profile diameter of the working circuit,the runner of the coupling has between 10 and 35% more vanes than theimpeller of the coupling, and the impeller has two sets of holes throughthe wall thereof, the centres of one set of holes being spaced from thecoupling axis by from 53 to 63% of the outer profile radius of theworking circuit and the centres of the second set of holes being spacedfrom the coupling axis by from 65 to 75% of the outer profile radius ofthe working circuit.
 2. A coupling according to claim 1, wherein thespacing between the two sets of holes is about 10%, measured in theradial direction of the coupling, of the radius of the outer profile ofthe working circuit.
 3. A coupling according to claim 1 wherein therunner has between 15 and 25% more vanes than the impeller.
 4. Acoupling according to claim 1, wherein the two sets of holes have pitchcircle diameters respectively substantially 58% and 70% of the outerprofile diameter of the working circuit, and the runner hasapproximately 20% more vanes than the impeller.
 5. A coupling accordingto claim 1, wherein the baffle has a diameter of substantially 1.3 timesthe inner profile diameter of the working circuit.
 6. A couplingaccording to claim 1, wherein the two sets of holes have pitch circlediameters respectively substantially 58% and 70% of the outer profilediameter, and the runner has between 15% and 25% more vanes than theimpeller.
 7. A coupling according to claim 6, wherein the baffle has adiameter of substantially 1.3 times the inner profile diameter of theworking circuit.
 8. A coupling according to claim 1, wherein the spacingbetween the two sets of holes is about 10%, measured in the radialdirection of the coupling, of the radius of the outer profile of theworking circuit, and wherein the runner has between 15% and 25% morevanes than the impeller.
 9. In a variablE filling fluid coupling havingvaned impeller and running elements together defining a toroidal workingcircuit for a liquid, comprising the improvement wherein the couplinghas a baffle of diameter greater than the inner profile diameter of theworking circuit to minimize the maximum torque generated by the couplingwhen driving a load, the runner of the coupling has between 10 and 35%more vanes than the impeller of the coupling, and the impeller has twosets of holes through the wall thereof, the centres of one set of holesbeing spaced from the coupling axis by from 53 to 63% of the outerprofile radius of the working circuit, and the centres of the second setof holes being spaced from the coupling axis by from 65 to 75% of theouter profile radius of the working circuit.
 10. A coupling according toclaim 9, wherein the runner has between 15% and 25% more vanes than theimpeller.
 11. A coupling according to claim 9, wherein the centres ofsaid one set of holes are spaced from the coupling axis by about 58% ofthe outer profile radius of the working circuit, and wherein the centresof said second set of holes are spaced from the coupling axis by about70% of the outer profile radius of the working circuit.
 12. A couplingaccording to claim 11, wherein the runner has about 20% more vanes thanthe impeller.